Three-Dimensional Porous HxTiS2 Nanosheet–Polyaniline Nanocomposite Electrodes for Directly Detecting Trace Cu(II) Ions

Research Progress in Enzyme Biofuel Cells Modified Using Nanomaterials and Their Implementation as Self-Powered Sensors

Enzyme biofuel cells (EBFCs) can convert chemical or biochemical energy in fuel into electrical energy, and therefore have received widespread attention. EBFCs have advantages that traditional fuel cells cannot match, such as a wide range of fuel sources, environmental friendliness, and mild reaction conditions. At present, research on EBFCs mainly focuses on two aspects: one is the use of nanomaterials with excellent properties to construct high-performance EBFCs, and the other is self-powered sensors based on EBFCs. This article reviews the applied nanomaterials based on the working principle of EBFCs, analyzes the design ideas of self-powered sensors based on enzyme biofuel cells, and looks forward to their future research directions and application prospects. This article also points out the key properties of nanomaterials in EBFCs, such as electronic conductivity, biocompatibility, and catalytic activity. And the research on EBFCs is classified according to different research goals, such as improving battery efficiency, expanding the fuel range, and achieving self-powered sensors.

Water-stable metal organic framework-199@polyaniline with high-performance removal of copper II

Metal organic frameworks (MOFs)-based adsorbents for copper ion (Cu²⁺) generally have the disadvantages of instability in water, low adsorption capacity, and selectivity. Aimed at such problems, we fabricated MOF-199 coated with polyaniline (MOF-199@PANI, core@shell) composite for specific adsorption of Cu²⁺ in water efficiently. Combined with the characterization by SEM, XRD, and FT-IR, the comprehensively excellent performance probably derived from porous structures of MOF-199, as well as the complexation between Cu²⁺ and the N atoms of imine moieties in PANI. In addition, the coating process by PANI perfectly protected the MOF skeleton. The isothermal data fitted well to Langmuir isotherm model, of which the calculated adsorption capacity reached 7831.34 mg/g. It was one or two orders of magnitude higher than some other new absorbent for Cu²⁺ including some carbon-based or organic adsorbents. On the basis of the optimization including pH value, temperature, and ratio of raw materials, the fabricated composite has realized the removal of the spiked Cu²⁺ in actual fresh water and industrial wastewater samples.

Fluorescence and Colorimetric Dual-Mode Ratiometric Sensor Based on Zr-Tetraphenylporphyrin Tetrasulfonic Acid Hydrate Metal-Organic Frameworks for Visual Detection of Copper Ions

As a special heavy metal ion, copper ions (Cu²⁺) play an indispensable role in the fields of environmental protection and safety. Their excessive intake not only easily leads to diseases but also affects human health. Therefore, it is particularly important to construct a facile, effective, and highly selective Cu²⁺ probe. Herein, a novel Zr-tetraphenylporphyrin tetrasulfonic acid hydrate (TPPS) metal-organic framework (ZTM) was fabricated using TPPS as the ligand and exhibited strong red fluorescence with a high quantum yield of 12.22%. In addition, we designed a ratiometric fluorescent probe by introducing green fluorescein isothiocyanate (FITC), which was not subject to environmental interference and had high accuracy. When exposed to different amounts of Cu²⁺, the fluorescence emission at 667 nm from ZTMs is remarkably quenched, while that at 515 nm from FITC is enhanced, accompanied by a change in the solutions' fluorescence color from red to green under a UV lamp. Besides, the ZTMs solutions display an excellent ratiometric colorimetric response for Cu²⁺ and produce an obvious color change (from green to colorless) that is visible to the naked eye. The fabricated ZTMs@FITC fluorescent probe exhibits distinguished performance for Cu²⁺ detection with linear ranges of 0.1 to 5 μM and 5 to 50 μM, as well as a low detection limit of 5.61 nM. Moreover, a colorimetric sensor based on ZTMs exhibits a good linear range from 0.1 to 20 μM for Cu²⁺ with the detection limit of 4.96 nM. Furthermore, the dual-signal ratiometric sensor has significant specificity for Cu²⁺ and is successfully applied for monitoring Cu²⁺ in water samples, which proves its practical application value in the environment and biological systems.

Free-electrodeposited anodic stripping voltammetry sensing of Cu(II) based on Ti3C2Tx MXene/carbon black

A proof-of-principle concept for free-electrodeposited anodic stripping voltammetry (ASV) sensing of Cu²⁺ is proposed by using Ti₃C₂T_x MXene/carbon black (Ti₃C₂T_x@CB) nanohybrids as electrode materials. Owing to the high adsorption and reduction capability of Ti₃C₂T_x towards Cu²⁺, Ti₃C₂T_x MXene enables Cu²⁺ to be immobilized and self-reduced directly to form Cu⁰ on the Ti₃C₂T_x@CB electrode surface. As a result an oxidation peak current appears from the re-oxidation of Cu⁰ via differential pulse voltammetry. Carbon black (CB) was introduced to prevent Ti₃C₂T_x Mxene aggregation and improve the related electron transfer as well as enhance their surface area. After optimizing various conditions, a considerable low limit of detection (4.6 nM) and a wide linear range (0.01-15.0 μM) for Cu²⁺ were achieved at the working potential from - 0.3 V to 0.0 V (vs SCE). Relative standard deviation (RSD) of eight individual Ti₃C₂T_x@CB electrodes is 3.72%, and the recoveries from tap water sample and lake water sample were in the ranges of 97.0-108% and 104-107%, respectively.

Logarithmic Data Processing Can Be Used Justifiably in the Plotting of a Calibration Curve

The article is a response to a recent opinion piece that log concentration values should not be applied in analytical chemistry. An essential aim in the development of analytical chemistry methods is to obtain more sensitive and accurate detection values. For the application of chemical analysis methods, the obtained experiment data need to fit with the mathematical functions in the first place. As influenced by different detection principles and analytical methods, data can be displayed in a coordinate system with two linear axes for linear function fitting, or the data can first be taken through a logarithmic transformation and then for function fitting. Using raw data or data after logarithmic transformation primarily depends on analytical principles, without special rules of data formats. For example, ultraviolet-visible spectrophotometric data are more suitable for direct linear fitting. However, enzyme-catalyzed reaction or electrochemical data in logarithmic form are more appropriate for function fitting. This transformation of data form will not affect the soundness of fit statistics; rather, it simplifies the complexity of function analysis and calculation, which are the essence of analytical chemistry. In this brief article, we provide justification and legitimacy of the application of logarithmic processing in various fields of quantitative analytical chemistry.

Highly sensitive detection of Pb2+ and Cu2+ based on ZIF-67/MWCNT/Nafion-modified glassy carbon electrode

A series of different facile modification layers (MLs) was designed to gradually increase the electrochemical sensing performance of glassy carbon electrode (GCE) for simultaneously detecting Pb²⁺ and Cu²⁺. ML designs were mainly a different combination of ZIF-67, MWCNT and Nafion, and their different electrochemical sensing performances were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), square wave stripping voltammetry (SWSV) and chronocoulometry. The fabricated sensor, which modified with ZIF-67/MWCNT and Nafion layer, exhibited the biggest response peak current to Pb²⁺ and Cu²⁺. In addition, it displayed a wide linear detection range of 1.38 nM-5 μM for Pb²⁺ and 1.26 nM-5 μM for Cu²⁺, a detection accuracy of about 1 nM for both Pb²⁺ and Cu²⁺, and an excellent stability for both Pb²⁺ and Cu²⁺. We also analyzed the real water sample taken from Changchun's Sanjia Lake and Yan Lake. We believe this ML design provides instruction for building high-performance electrochemical sensing systems.

Covalent functionalization of MoS2 nanosheets synthesized by liquid phase exfoliation to construct electrochemical sensors for Cd (II) detection

Surface functionalization is an effective strategy in the precise control of electronic surface states of two-dimensional materials for promoting their applications. In this study, based on the strong coordination interaction between the transition-metal centers and N atoms, the surface functionalization of few-layer MoS₂ nanosheets was successfully prepared by liquid phase exfoliation method in N, N-dimethylformamide (DMF), 1-methyl-2-pyrrolidinone, and formamide. The cytotoxicity of surface-functionalized MoS₂ nanosheets was for the first time evaluated by the methylthiazolyldiphenyl-tetrazoliumbromide assays. An electrochemical sensor was constructed based on glass carbon electrode (GCE) modified by MoS₂ nanosheets obtained in DMF, which exhibits relatively higher sensitivity to Cd²⁺ detection and lower cytotoxicity against MCF-7 cells. The mechanisms of surface functionalization and selectively detecting Cd²⁺ were investigated by density functional theory calculations together with various spectroscopic measurements. It was found that surface-functionalized MoS₂ nanosheets could be generated through Mo-N covalent bonds due to the orbital hybridization between the 5 s orbitals of Mo atoms and the 2p orbitals of N atoms of the solvent molecules. The high selectivity of the sensor is attributed to the coordination reaction between Cd²⁺ and O donor atoms of DMF adsorbed on MoS₂ nanosheets. The robust anti-interference is ascribed to the strong binding energy of Cd²⁺ and O atoms of DMF. Under the optimum conditions, the electrochemical sensor exhibits highly sensitive and selective assaying of Cd²⁺ with a measured detection limit of 0.2 nM and a linear range from 2 nM to 20 μM.

Two-dimensional transition metal dichalcogenide/conducting polymer composites: synthesis and applications

The exploration of hybridizing transition metal dichalcogenide (TMD) nanosheets with other materials as a unique approach for engineering their properties has attracted considerable attention from the scientific community for both basic studies and numerous potential applications. Among the various kinds of functional materials in hand, the utilization of intrinsically conducting polymers (CPs) in the construction of advanced hybrid composites with TMD nanosheets is considered as a fascinating approach. In this review, we aim at providing a survey of the literature on recent progress in composites based on 2D TMD and CPs. In this regard, we first discuss the different synthetic strategies used for the fabrication of two-dimensional transition metal dichalcogenide/conducting polymer (2D TMD/CP) composites in detail. Subsequently, we demonstrate the state-of-the-art advances in the utilization of these novel composites in promising applications such as energy storage, sensing devices, hydrogen production and so on. Finally, we also highlight some perspectives on the major challenges and future directions in this field of research.